Elemental phosphorus is a very pyrophoric material which ignites spontaneously when exposed to air. It is common practice to store elemental phosphorus wastes under water in waste ponds to prevent their contact with the atmosphere and thereby cause pyrotechnic incidents.
U.S. Pat. No. 4,492,627 to D. A. Orea describes a process for recovery of elemental phosphorus from waste ponds by dredging the waste pond to obtain an aqueous phosphorus slurry, separating particles larger than about 2 mm from the slurry, treating the remaining slurry in an initial hydrocyclone and removing an overflow of solids larger than 500 micrometers, treating the underflow from the initial hydrocyclone in a smaller diameter hydrocyclone, removing a second overflow enriched in slimes and diminished in phosphorus, removing a second underflow enriched in phosphorus and diminished in slimes and heating it sufficiently to melt the phosphorus contained therein, treating the heated second underflow in a centrifugal separator, and separating and recovering a stream of coalesced phosphorus from a heavy fraction of impurities.
U.S. Pat. No. 4,608,24I indicates that phosphorus-containing wastes can be recycled to a phosphorus furnace for burning in air.
Finally, "A Waste Recovery Story" by J. C. Barber et al., which appeared in Chemtech, May I986, pages 298-302, indicates that phosphorus sludge can be kept submerged in ponds to prevent it from burning. It also indicates that a process has been proposed for separating elemental phosphorus from the solids, wherein phosphorus and water are distilled off, leaving a solid residue which contains no elemental phosphorus. The residue, which contains relatively high amounts of P.sub.2 O.sub.5, is fed back to a furnace. It also proposes a process in which the phosphoruscontaining waste would be oxidized with air and hydrated with water to make a mixture of acids suitable for use in preparing agglomerated feed materials. Phosphate ore or reducing carbon could be agglomerated by the thus described low-temperature process, and the toxic chemicals could be smelted according to this publication.